Electron multiplier



Sept. 24, 1957 N. c. FULMER ELECTRON MULTIPLIER Filed April 17?', 19541JNVENTOR. NORMAN c. F-ULMER v ATTORNEYS aperture 14 therein.

United States Patent ELECTRON MULTIPLIER Norman C. Fulmer, Pearl River,N. Y., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. J.,a corporation of Delaware v Application April 13, 1954, Serial No.422,900

Claims. (Cl. 313-105) This inventionrelates to electron multipliers ofthe type in which dynodes are employed between a cathode and an anodefor the purpose of multiplying or increasing electrons.

It is an object of the invention to provide an electron multipliercapable of functioning in a magnetic field. Another object is to providean electron multiplier so constructed that a plurality of electronmultipliers may be arranged in a camera pick-up tube for colortelevision, so as to function as electron-multiplying targets for colorsignals. Other objects will be apparent.

In the drawing:

Fig. 1 is a cross-sectional view of the side of the electron multiplier;

Fig. 2 is a cross-sectional view of the device taken on the line 2-2 ofFig. l; and

Fig. 3 is a schematic diagram of preferred electrical connections to theelectron multiplier elements.

The invention is particularly applicable for use in the color pick-uptube shown and described in the Neal Diepeveen patent application,Serial Number 369,888, in which there is shown a means for derivingelectrons from a photocathode in a color television camera tube, meansfor scanning the electrons across an apertured plate, and magnetic fieldmeans for separating the electrons which pass through the aperture intorespective color-representative signals.

In the drawing, vsuch a tube as described above is shown, having anelectric coil or magnetic means 11 for producing a magnetic fieldtherein. The tube 10 also comprises the photocathode 12 and a plate 13with an Representative electrons 15 pass through the aperture 14 andenter into the magnetic field 16. The magnetic field 16 causes theelectron beam 15 to curve downwardly and to separate into. a pluralityof electron beams 17, 18 and 19, these different beams beingrepresentative, respectively, of differing colors of light whichproduced the electrons on the photocathode 12 in the camera tube. Forexample, the electrons 15 which have been omitted from the photocathodedue to excitation by red light, will have a relatively low velocity andwill be curved, by the magnetic eld 16, on a relatively short radius, asindicated at 17. The electrons which are emitted from thephotocathodedue to excitation by green light, will have an intermediatevelocity and will be curved on an intermediate radius in the magneticiield 16, as indicated at 18. Electrons 15,

which are emitted from the photocathode due to excitation by blue light,Will have a relatively high velocity and thus will be curved on arelatively large radius in the magnetic field 16, as indicated at 19.

In accordance with the present invention, the redrepresentativeelectrons 17 are collected by an electron multiplier target 21; thegreen-representative electrons 18 are collected by an electronmultiplier target 22; and the blue-representative electrons 19 arecollected by an electron multiplier target 23. These targets aresomewhat circular, as shown in Fig. 2, and each comprises a g 2,807,741Patented. Sept. 24, .1957

circular shield housing 26 having an opening 27 near the center thereofthrough which the electrons 15 may pass to strike a cathode or firstdynode 28, which is of a material which will produce secondary electronswhen struck or excited by primary electrons. The opening 27 in thecenter of each electron multiplier housing 26 permits electrons to passthrough the other electron multipliers 21 or 22, in order to strike thefollowing electron multipliers 22 or 23.

Fig. 2 is a sectional view of one representative electron target unit23, such as blue; only the blue-representative electrons 19 are shown asthey enter the opening 27. The cathode 28 is positioned so as to bestruck by such blue-representative electrons 19.

A plurality of secondary-emissive dynodes 29, 30 and 31, and an outputanode 32, are arranged circularly in order within the field housing 26and about the axis of the electron beam .15.

As shown in Fig. 3, a source 36 of voltage is connected to the cathode28, dynodes 29, 30, 31 and anode 32 through series-connectedvoltage-dropping resistors 41-45. The resistor 41, between the highvoltage and the anode 32, functions as an output load impedance. Outputterminals 46, 47 are connected respectively to the' anode 32 and to thecathode 28.v

As illustrated in Fig. 2, the electrons 19 strike the cathode 28,causing secondary electrons 51 to be emitted therefrom. l Thehigher-positive polarity voltage on the first dynode 29 causes thesecondary electrons 51 to strike the first dynode 29, resulting ina'larger number of secondary electrons 52 to be emitted therefrom.Similarly, still greater numbers of secondary electrons 53 'and 54 areemitted from the second and third dynodes 30, 31. The greatly multipliednumber of electrons 54 strike the anode 32, and cause an amplifiedoutput signal to be developed across the load impedance 41 and at theterminal 46.

The electron-multiplier targets 21 and 22 are each constructed similarlyto the structure of the target 23, which has been described.

The targets 21, 22 and 23 are tilted as shown, so that the cooperativeeffects of the electrostatic fields produced by the voltages on thedynodes and anodes, and the magnetic field 16 produced by the magnets11, will be such as to cause the secondary groups of electrons 51, 52,53, 54, to strike the proper dynodes and anode. When electrons movethrough a magnetic field perpendicular to the ux lines, the motion ofthe electrons will become curved at right angles to the flux lines.Accordingly, the magentic field flux 16 will cause the secondary groupsof electrons 51, 52, these groups of electrons moving in an upwarddirection, to deflect towards the front end 56 of the tube 10. However,with the top ends of the targets 21, 22 and 23 tilted towards the frontend 56 of the tube in accordance with this invention, the dynodes 29 and30 are properly positioned so that the magentically-dellected electrongroups 51, 52 will properly strike the dynodes 29, 30.

The dynodes 30 and 31 are positioned symmetrically, i. e., withoutrelative longitudinal displacement. vNo compensation is necessary here,because the group 53 of secondary electrons moves substantially parallelto the magnetic uX lines 16 and, hence, there will be no magneticdeflection ofthe electrons 53. The downwardly moving secondary electrons54 will be caused, by the magnetic flux 16, to be deflected toward therear end 57 of the tube 10. However, it will be noted that the tilt ofthe targets 21, 22, 23, is such that the anode 32 is olset rearwardly ofthe position of the dynode 31, so that the electrons 54 which aredeflected rearwardly by the magnetic field 16 will properly strike theanode 32. As shown in Fig. 1, the mutually adjacent edges 6162, 63-64etc. of the cathode 28, dynodes 29-31 and anode 32, are dispersedsubstantially parallel with the axis 66 of the electron beam 15. Thisarrangement of the edges of the cathode, dynodes, and anode, tends tocause theelectrostatic elds between these elements tobe in a more nearlyvertical alignment than would be the case if the adjoining edges ofthese elements were perpendicular to the tilted planes of the targets21, 22 and 23. The effect of the aforementioned more nearly verticalelectrostatic fields tends to counteract partly the horizontaldeflection of the secondary electrons 51, 52 and 54, caused by themagnetic field 16.

It will be appreciatedthat the invention provides a compact arrangementof electron-multiplying elements, the arrangement permitting a beam ofprimary electrons Vto pass through some of the electron multiplier unitsso as to activate the cathodes of other electron multiplying units. Theinvention also achieves electron-multiplication in a magnetic eld, byvirtue of utilizing the effect of the magnetic eld to help guide, incooperation with electrostatic lields, secondary electrons to the properdynodes or anode.

While a preferred embodiment of the inventionhas been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art. The scope of the invention is dened in the followingclaims.

What is claimed is:

1. An electron multiplier tube comprising a source of electrons, meansto accelerate said electrons to form an electron beam, an electronmultiplier structure having elements comprising a cathode, a pluralityof dynodes and an anode circularly arranged around the axis of saidelectron beam and lying in a plane tilted with respect to said axis, andmeans producing a magnetic field per pendicularly through said tube tocause said electron beam to deect and strike said cathode.

2. The structure in accordance with claim l, the mutually adjoiningedges of said elements being sub stantially parallel to said axis.

3. An electron multiplier system comprising means for producing a beamof electrons, and an electron multiplier structure having elementscomprising a cathode,` a plurality of dynodes and an anode arrangedsubstantially circularly around said axis and means producing a magneticfield perpendicular to the axis of said electron beam to deflect saidelectrons to strike said cathode, the plane of said electron multiplierstructure being tilted with respect to said axis.

4. The device in accordance with claim 3, in which each of said elementsextends substantially parallel to said axis, the mutually adjoiningedges of said elements being substantially parallel to said axis.

5. An electron multiplier tube comprising means `for producing anelectron beam, a plurality of multiplier targets, each of said targetshaving an anode, a cathode, and a plurality of dynodes encircling theaxis of said beam, said plurality of targets disposed along the axis ofsaid beam.

References Cited in the le of this patent UNITED STATES PATENTS2,225,786 Langenwalter et al. Dec. 24, 1940 2,231,676 Muller Feb. 11,1941 2,238,607 Schnitger Apr. 15, 1941

